The present invention relates to a dielectric ceramic composition, a multi-layer ceramic capacitor using the same, and more particularly to a dielectric ceramic composition having superior dielectric properties, a multi-layer ceramic capacitor using a nickel or nickel alloy as internal electrodes, and manufacturing method therefor.
As shown in FIG. 1, the multi-layer ceramic capacitor generally includes a ceramic chip having a plurality of ceramic dielectric layers 2a and 2b and a plurality of internal electrodes 3, in which the dielectric layers and the internal electrodes are alternately stacked, and a pair of external electrodes 4 electrically connected to both sides of said ceramic chip. The internal electrodes are made of a base metal such as Ni or Ni alloys instead of the expensive metals such as Ag, Pd and the like to reduce the cost of manufacturing multi-layer ceramic capacitors.
Recently, the progress of the electronic technology has promoted the miniaturization of the electronic components, and there is a trend for the multi-layer ceramic capacitors to become larger in capacitance and better in thermal stability for its capacitance. Such a requisite is same in the multi-layer ceramic capacitor with the Ni electrodes. If the multi-layer ceramic capacitor with the Ni electrodes is to meet the requisites of large capacitance and miniaturization, the dielectric layer has to be thinner and has to consist of more multiple layers. However, in the conventional dielectric materials, when the dielectric layers are made very thin, the layers are applied by higher voltage even with the same voltage, resulting in lower dielectric constant, the aggravation of the temperature dependence of the capacitance, and the deterioration of other properties. Particularly, if the thickness of the dielectric layer is reduced down to 5 xcexcm, the number of the ceramic grains present between the internal electrodes is reduced to 10 or less, and therefore, a high stability cannot be expected.
Meanwhile, conventionally barium titanate has been used as the dielectric layer. The typical examples are disclosed in U.S. Pat. Nos. 5,335,139, 5,362,693, 5,403,797, 5,600,533, 5,646,080, 5,668,694, 5,858,901, 5,862,034, 5,877,934 and 6,008,981. However, if barium titanate is sintered under a reducing atmosphere, it becomes a semiconductor during the sintering. Anti-reduction shells therefore are required to be formed on the surfaces of all the grains of the barium titanate. Otherwise the insulating properties might be aggravated, while the life expectancy would be drastically reduced. Further, even if the shells with high insulation resistance are formed, when their thickness is thin, then barium titanate becomes a semiconductor, with the result that the insulating properties are aggravated, as well as shortening the life expectancy. Accordingly, if the capacitor is to be manufactured with a dielectric composition in which the main ingredient is barium titanate, then much time and expense are required to make the composition uniform.
In order to solve this problem, Korean Patent Laid-open No. 2000-17250 discloses a capacitor in which barium calcium titanate with the anti-reduction properties greatly improved is used as the starting material, and the electrodes are made of Ni. Barium calcium titanate has a high anti-reduction property owing to the fact that Ti is replaced with Ca, thereby creating a lattice defect. Accordingly, barium calcium titanate can maintain a high insulating resistance even if the shells cannot be formed during the sintering or even if the shells are thinly formed. A multi-layer ceramic capacitor with the electrodes of Ni in the above cited Korean Patent Laid-open is made of a dielectric composition in which the starting material is (Ba1-xCax)mTiO2, and the minor ingredient is a glass oxide. Thus the drop of the dielectric constant is low, and the temperature characteristics meet the X7R of the EIA standard. Further, in another dielectric ceramic capacitor of the above cited Korean patent application, one or more of the rare earth metals Re is contained in (Ba1-xCax)mTiO2 where Re is Y, Gd, Th, Dy, Ho, Er or Yb. Thus owing to the diffusion during the sintering, core shells with the rare earth metal components are formed on or near the grain boundaries.
The multi-layer ceramic capacitors that contain glass component in the dielectric layer as one of miner ingredients show their high insulating resistance. However, glass component in such capacitors may affect the diffusion rate of the other composition which are diffused into their cores and form low dielectric constant shells. Accordingly, this capacitors show rather a low dielectric property. Particularly, in the above cited patent application, the minor ingredient is sintering agents such as Li2Oxe2x80x94(Si, Ti)O2xe2x80x94MO oxide (where MO is at least one selected from among Al2O3 and ZrO2), or SiO2xe2x80x94TiO2xe2x80x94XO oxide (where XO is at least one selected from the group consisting of BaO, CaO, SrO, MgO, ZnO and MnO), or Li2Oxe2x80x94B2O3xe2x80x94(Si, Ti)O2, or Al2Oxe2x80x94MOxe2x80x94B2O3 (where MO is at least one selected from the group consisting of BaO, CaO, SrO, MgO, ZnO, and MnO). However, such sintering agents exist in liquid phase at a low temperature, and therefore, most of them shows a dielectric constant of less than 2000, thereby making it impossible to provide a reliable multi-layer ceramic capacitor. Further, in order to meet the X7R, if the product is manufactured by individually mixing a plurality of minor ingredients to the main ingredient, the shell ingredients can become diverse, and therefore, the deviation of the electrical properties is enlarged, with the result that the yield is decreased.
The present invention is intended to overcome the above-mentioned disadvantages of the conventional techniques.
Therefore it is an object of the present invention to provide a dielectric ceramic composition in which BaCaxTiO3(0 less than xxe2x89xa60.02) with a superior anti-reduction property is used, and the diffusion rate within the dielectric ceramic chip is more efficiently controlled, so that the X7R standard can be met, and that the dielectric properties would be superior.
It is another object of the present invention to provide a multi-layer ceramic capacitor in which the above described dielectric ceramic composition and Ni electrodes are used.
It is still another object of the present invention to provide a method for manufacturing the multi-layer ceramic capacitor in which the deviation of the dielectric properties is small.
In achieving the above objects, the dielectric ceramic composition according to the present invention includes:
100 moles of barium calcium titanate BaCaxTiO3(0.001xe2x89xa6xxe2x89xa60.02),
0.5-4 moles of Mg,
0.01-0.5 moles of MnO,
0.1-2 moles of BaO,
0.1-2 moles of CaO,
1-4 moles of SiO2 and
0.1-3 moles of at least one or more compounds selected from the group consisting of Y2O3, Dy2O3, Ho203 and Er2O3.
In another aspect of the present invention, the dielectric ceramic composition can include 0.4 moles or less of V2O5 and/or Cr2O3.
In still another aspect of the present invention the multi-layer ceramic capacitor according to the present invention includes:
a plurality of dielectric ceramic layers composed of the above dielectric ceramic composition;
a plurality of internal electrodes disposed on the dielectric ceramic layers, the internal electrodes and the dielectric ceramic layers being alternately stacked to form a stacked chip; and
a pair of external electrodes formed on both sides of the stacked chip.
In still another aspect of the present invention, the method for manufacturing a multi-layer ceramic capacitor according to the present invention includes the steps of:
preparing ceramic powders comprising
0.5-4 moles of MgO,
0.01-0.5 moles of MnO,
0.1-2 moles of BaO,
0.1-2 moles of CaO,
1-4 moles of SiO2 and
0.1-3 moles of at least one or more compounds selected from the group consisting of Y2O3, Dy2O3, Ho203 and Er2O3,
per 100 moles of barium calcium titanate BaCaxTiO3(0.001xe2x89xa6xxe2x89xa60.02), wherein at least two or more kinds of the ceramic powders are mixed and calcined;
crushing the calcined powders, mixing the calcined powders and remaining powders with barium calcium titanate, and adding a binder and a solvent so as to form a slurry;
forming the slurry into a plurality of sheets, and printing Ni or an Ni alloys onto some of the sheets so as to form internal electrodes;
stacking alternately the sheets with and without the internal electrodes, whereby a stacked chip is formed, and sintering the chip; and
disposing a pair of external electrodes on both sides of the stacked chip so as to be connected to said internal electrodes, whereby a multi-layer ceramic capacitor with a low deviation of dielectric properties is formed.